Effects of physical heterogeneity on the adsorption of poly(ethylene oxide) at a solid-liquid interface

Experiments on the adsorption of PEO from aqueous solutions onto planar sur faces that are physically heterogeneous but chemically homogeneous are pres ented. Gold substrates that differ only in the degree of roughness were pre pared by thermal evaporation on glass and by template stripping from mica. To ensure a similar chemical interface, the gold substrates were modified w ith a self-assembled monolayer of a long chain alkanethiol (CH3(CH2)(11)SH) . The kinetics of adsorption of PEO were monitored using a surface plasmon resonance technique with high time resolution. The experimental measurement s demonstrated that higher adsorbed amounts and lower chain distortion acco mpanied an increase in surface roughness. These are the first systematic ex perimental measurements that substantiate past theoretical predictions of p olymer adsorption on random surfaces. Kinetic studies revealed that the ini tial rate of adsorption was proportional to bulk concentration on both roug h and smooth substrates, but the PEO adsorbed more readily on the rougher s urfaces.